The normal, healthy human vagina is weakly acidic and has a pH of approximately 4.5. This acidic condition of the vagina provides an effective barrier against the growth of pathogenic microorganisms normally associated with vaginal infection, because such microorganisms do not grow below a pH of about 5. If, however, the pH of the vagina becomes less acidic, i.e., higher than about 5, pathogenic microorganisms tend to multiply.
A change in pH of the vagina from the normal of about 4.5 to 5 to a more alkaline pH may be brought about by various vaginal conditions and may occur at any time during the menstrual cycle. During menstruation, in particular, the vagina becomes less acidic due to the presence of menstrual fluid which has a pH of from about 7 to 8. As a result, the protective barrier provided by the normal acidic condition of the vagina becomes less effective, thereby providing an environment favorable to the growth of the pathogenic microorganisms.
To overcome the reduction in acidity of the vagina and to re-establish the desired normal acidic condition, different formulations and techniques have been developed. Such efforts have included the development of formulations such as solutions, jellies, powders, suppositories, and the like containing acidifying materials which are introduced into the vagina in their prepared form.
While the above-mentioned types of products have met with acceptance, they are subject to numerous disadvantages. The solutions, jellies, powders, and suppositories containing acidifying materials may be inconvenient to handle and apply and are not fully retained in the vagina and tend to leak. In addition, they do not have capacity for absorbing vaginal fluid which may be present in the vagina, particularly during menstruation. Therefore, to use such products during menstruation, it is also necessary to use at the same time a catamenial tampon or similar article.
Other attempts to lower the pH have included physically incorporating acidifying materials into absorbent products by coating, spraying, impregnating and the like, to impart to such products acidifying properties.
U.S. Pat. No. 4,431,427 to Lefren et al, discloses a tampon having incorporated therein one or more organic acids in combination with at least one of oligomer and polymer derivatives of the acids. The acids may be citric, gylcolic, malic, tartaric or lactic acids. The tampon is intended for maintaining a pH of about 4.5 to 2.5 in the fluids absorbed by the tampon during use, thereby inhibiting the growth of pathogenic bacteria in the tampon.
U.S. Pat. No. 4,661,101 to Sustmann discloses a catamenial tampon comprising a microbistatic fibrous absorbant core and an outer covering layer of a pH-regulating fibrous, cellulose material. The cellulose fibers are modified by carboxymethyl groups which are converted into their free acid form by treatment with an acid.
WO 91/08726 discloses a disposable sanitary napkin comprising a water permeable topsheet, an absorbent core and a water impermeable backsheet. The topsheet and/or backsheet comprise absorbable, hydrolyzable and biodegradable substances such as a lactic acid-based or glycolic acid-based polyester. This enhances the disposability of the napkin.
U.S. Pat. No. 6,020,453 to Larsson et al, discloses an absorbent article having a surface material, wherein the surface material includes a surface layer (being the outermost layer) which comprises a lactic acid-based polyester. The surface material is capable of excreting lactic acid to the surrounding urogenital region of menstruating women so as to establish a pH value of at most 4.0. The polyester has a molecular weight of at most 50,000 and the monomer/oligomer concentration is 5-30% by weight.
WO 02/17981 and U.S. 2002/0045873 discloses a formulation effective in reducing the pH in a menstruating vagina or in a tampon inserted therein to below pH 5.5 comprising: (a) 3-80% by weight of a solid organic acid polymer; (b) 92-15% by weight of a solid organic acid; and (c) 5-30% of a wetting agent. In a preferred embodiment, the organic acid polymer is a polymer of lactic acid. Preferred polymers are L-lactide or DL-lactide (LD), a racemic mixture of a cyclic dimer of lactic acid, and polylactic acid (PLA) in the general range of 200-2000 MW.
Glycolide is a cyclic dimer of glycolic acid, containing two ester groups which upon contact with an aqueous environment are hydrolyzed, resulting in two glycolic acid molecules.